NEW YORK — The accountant for some of Bernard Madoff's wealthiest former clients pleaded guilty Tuesday to actions that aided the Ponzi scheme mastermind's massive scam.

Paul Konigsberg, 78, admitted he was present in 2003 when Madoff assistant Annette Bongiorno changed annual account statements for one client, and subsequently filed a false tax return using the altered data.

This "was wrong, and I knew it at the time," said Konigsberg, dressed in a gray suit and blue-checked tie as he spoke in Manhattan federal court. However, he said he "was not aware of Madoff's horrific and evil Ponzi scheme, which has brought great suffering to so many."

During a 48-minute hearing before U.S. District Court Judge Laura Taylor Swain, the Connecticut accountant and lawyer pleaded guilty to conspiracy, falsifying records of a broker-dealer and falsifying records of an investment adviser.

He faces a potential maximum prison term of 30 years, plus heavy financial penalties, including $4.4 million in forfeiture and more in restitution.

Swain set a tentative Sept. 19 sentencing date.

His plea agreement indicated Konigsberg is cooperating with prosecutors, which appeared to raise the possibility of Madoff-related cases yet to come. The six-year federal statute of limitations on tax crimes stemming from the Ponzi scheme has not yet expired.

Prosecutors and defense lawyer Reed Brodsky declined to comment.

Konigsberg is charged separately in a parallel civil lawsuit filed last year by the Securities and Exchange Commission. That proceeding has been on hold pending completion of the criminal case.

The accountant is the latest in a string of suspects who either pleaded guilty or were convicted at trial of aiding the decades-long scam Madoff used to enrich himself and others while defrauding thousands of average investors, charities, celebrities and others.

Victims in the U.S. and around the world lost an estimated $20 billion, upending their life plans and leaving some near destitution.

The scam collapsed in December 2008 when clients began trying to get their money back amid financial fallout from the Great Recession. Madoff, now 76, pleaded guilty without standing trial the following year. He's now serving a 150-year federal prison term.

Konigsberg was the senior tax partner at the former New York-based Konigsberg Wolf accounting firm. He handled accounting work for Madoff clients who collectively held more than 300 investment accounts. On top of what those clients paid him, he received $15,000 to $25,000 in monthly payments from Madoff's investment business for more than a decade, said Assistant U.S. Attorney Matthew Schwartz.

Konigsberg was also the only person outside Madoff relatives to hold an ownership interest in one of the scam mastermind's investment businesses.

He was arrested on Sept. 26, and initially pleaded not guilty. At the time, Brodsky said Konigsberg had been hoodwinked by Madoff and was one of the disgraced financier's many victims.

But Konigsberg changed his plea after the criminal convictions in March of Bongiorno and four other former Madoff employees who unsuccessfully employed a similar defense at trial. They are scheduled to be sentenced in late July.

Madoff's personal accountant, David Friehling, pleaded guilty in 2009 and testified as a federal prosecution witness in that trial.